Fitness contours (Yield strength (ε) – Mutation probability (x)) for rare disease variants in the presence of non-replicators under varying degrees of kin competition.

(A) α = 0.75, (B) α = 1.0, (C) α = 5.0. Increasing effects of kin competition can reduce optimal levels of relatedness and favour disease variants that produce fewer numbers of infectious pathogens (reduced yield). [Shading: black (low fitness) to white (high fitness)]. (Fitness is the dominant eigenvalue from equation 12).